1. Field of the Invention
The present invention relates to a method of extracting feature image data and a method of extracting person's face data, more particularly to a method of extracting feature image data and a method of extracting person's face density data used to copy a color original image to a color copying material or black-and-white copying material.
2. Description of the Related Art
A person's face is the most closely examined part of a portrait. To finish a high-quality photo, it is necessary to print the person's face with a proper color.
Conventionally, the face region in the original image of a color film is specified by a light pen to extract the data for the density of a person's face and the exposure is determined so that the face color is properly printed according to the extracted density data. This type of art is disclosed in the official gazettes, e.g., Japanese Patent Application Laid-Open Nos. 62-115430, 62-115431, 62-115432, 62-189456, 62-189457, 63-138340, and 63-178222.
However, the above related art has a problem that printing requires a lot of time because the operator has to specify the face region for each image by a light pen. Moreover, it is difficult to realize automation because the operator has to visually specify the face region.
Official gazettes, i.e., Japanese Patent Application Laid-Open Nos. 52-156624, 52-156625, 53-12330, 53-145620, 53-145621, and 53-145622, disclose the following method of extracting the data for person's face by extracting flesh-color data.
That is, an color original image is divided into many photometric points, each photometric point is resolved into three colors of R (red), G (green), and B (blue) to photometrically measure them, and it is judged if the color of each photometric point calculated from photometric data is kept within the flesh-color range. Then, a cluster (group) of the photometric points decided as a color within the flesh-color range is used for face density data.
For this method, however, because colors within the flesh-color range are assumed to be face density data, flesh color of ground, trunk of a tree, and clothes, or portions other than face having a color similar to flesh color are extracted as face density data. Moreover, when the same object is photographed under the same condition, it may not be possible to automatically extract face density data if the type of film differs because the color tone differs in photographed images. Furthermore, when the color of a light source for illuminating an object differs, it may not be possible to automatically extract face density data if the color of the light source differs because the color tone of a photographed image differs (for example, an image photographed by using a fluorescent light for the light source shows green tone).
To solve the problem caused by the difference of light-source color, it is only necessary to correct the light-source color before extracting photometric data within the flesh-color range. The light source can roughly be classified into sunlight, fluorescent light, and tungsten light. The color tone of sunlight depends on the season and time zone and also on direct or indirect light even if the season and time zone are the same.
Artificial light such as fluorescent light has various color tones because products are diversified. Therefore, it is difficult to correct the light source by specifying the type of light source for each light source. Even if light source correction can completely be performed, it is impossible to avoid extracting flesh color of ground and trunk of a tree or portions with a color similar to flesh color. Therefore, it is impossible to take action when the type of film differs.